From my experience In brazilian jiu jitsu any time your opponents neck or head is near your mid section you can get your arm around the head or neck because it is completely exposed, even if your unable to get under the chin a head crank hurts like hell

There is no unique picture of reality. Stephen Hawking

1 Timothy 2:12 But I suffer not a woman to teach, nor to usurp authority over the man, but to be in silence.

This is like my go-to takedown. My coaches love this one. Most of the time I use it from the clinch though and use my lead leg, and I post the foot once it's around and then pressure with my shoulder on the way down into half guard. Sometimes you can use your right hand on the thigh or knee to then block the opponent's left leg and shimmy into a low mount from there.